Electric and magnetic fieldsEdexcel A-Level Physics: Topic test

20 questions, 54 marks

Edexcel A-Level Physics

Electric and magnetic fields topic test

Total 54 marks

Name

Class

Date

1
In a simple model of a hydrogen atom, an electron is at a distance of 5.3 × 10⁻¹¹ m from a proton. Treat both particles as point charges in a vacuum. The elementary charge is 1.60 × 10⁻¹⁹ C.
(a)
What is the magnitude of the electrostatic force between the electron and the proton?
[1 mark]
A5.1 × 10¹¹ N
B4.1 × 10⁻⁸ N
C8.2 × 10⁻⁸ N
D1.6 × 10⁻⁷ N
(b)
What is the magnitude of the electric field strength produced by the proton at the position of the electron?
[1 mark]
A5.1 × 10¹¹ N C⁻¹
B8.2 × 10⁻⁸ N C⁻¹
C1.3 × 10⁻²⁶ N C⁻¹
D27 N C⁻¹
(c)
The distance between the electron and the proton is doubled. Calculate the new force between them.
[2 marks]
Total for question 1: 4 marks
2
A point charge of −5.0 nC is fixed in a vacuum. Take the electric potential at infinity to be zero.
(a)
What is the electric potential at a point 0.20 m from the charge?
[1 mark]
A+2.2 × 10² V
B−2.2 × 10² V
C−1.1 × 10³ V
D−1.1 × 10² V
(b)
What is the change in electric potential energy when a charge of +2.0 nC moves from infinity to a point 0.20 m from the fixed charge?
[1 mark]
A+4.5 × 10⁻⁷ J
B−9.0 × 10⁻⁷ J
C−2.2 × 10⁻⁶ J
D−4.5 × 10⁻⁷ J
(c)
Describe the shape of the equipotential surfaces around the point charge and state how they are oriented relative to the electric field lines.
[2 marks]
Total for question 2: 4 marks
3
A defibrillator contains a capacitor of capacitance 70 μF that is charged to a potential difference of 5.0 kV.
(a)
Calculate the charge stored on the capacitor and the energy stored in it.
[3 marks]
(b)
During a shock, 80% of the stored energy is delivered to the patient in 5.0 ms. Calculate the mean power delivered and the potential difference across the capacitor after the shock.
[4 marks]
Total for question 3: 7 marks
4
A 680 μF capacitor, charged to a potential difference of 8.0 V, is discharged through a 15 kΩ resistor. The plates of the capacitor are 0.50 mm apart and the field between them may be treated as uniform.
(a)
Calculate the time constant of the circuit, the initial charge stored and the initial current. Calculate the time taken for the potential difference across the capacitor to fall to 2.0 V.
[6 marks]
(b)
Calculate the energy dissipated in the resistor as the potential difference falls from 8.0 V to 2.0 V. Calculate the electric field strength between the plates when the potential difference is 2.0 V, and state how this field strength changes with time during the discharge.
[6 marks]
Total for question 4: 12 marks
5
An alpha particle, of charge +3.2 × 10⁻¹⁹ C, moves at 3.0 × 10⁵ m s⁻¹ and enters a uniform magnetic field of flux density 0.40 T. Its velocity makes an angle of 30° with the direction of the field.
(a)
What is the magnitude of the magnetic force on the alpha particle?
[1 mark]
A9.6 × 10⁻¹⁵ N
B3.3 × 10⁻¹⁴ N
C3.8 × 10⁻¹⁴ N
D1.9 × 10⁻¹⁴ N
(b)
A proton enters the same field with the same velocity. How does the magnetic force on the proton compare with the force on the alpha particle?
[1 mark]
AIt is the same.
BIt is half as large.
CIt is twice as large.
DIt is one quarter as large.
(c)
Explain why the speed of the alpha particle does not change while it moves in the field.
[2 marks]
Total for question 5: 4 marks
6
A circular coil of 120 turns and radius 4.0 cm is placed with its plane perpendicular to a uniform magnetic field. The flux density of the field decreases uniformly from 0.80 T to 0.20 T in 0.30 s.
(a)
What is the initial flux linkage of the coil?
[1 mark]
A0.48 Wb
B4.0 × 10⁻³ Wb
C1.9 Wb
D0.36 Wb
(b)
What is the magnitude of the e.m.f. induced in the coil?
[1 mark]
A0.010 V
B0.36 V
C1.2 V
D1.6 V
(c)
State and explain the direction of the magnetic field produced by the induced current in the coil, using Lenz's law.
[2 marks]
Total for question 6: 4 marks
7
A hair dryer is rated at 1800 W when it is connected to a sinusoidal alternating supply of r.m.s. potential difference 120 V and frequency 60 Hz.
(a)
Calculate the peak potential difference of the supply and the peak current in the hair dryer.
[3 marks]
(b)
Calculate the period of the supply and the peak power of the hair dryer. Explain why the mean power is not equal to the peak power.
[4 marks]
Total for question 7: 7 marks
8
A coil of 300 turns and area 2.0 × 10⁻³ m² rotates at a steady 50 revolutions per second in a uniform magnetic field of flux density 0.10 T, about an axis perpendicular to the field. The ends of the coil are connected through slip rings to a 25 Ω resistor. The resistance of the coil is negligible.
(a)
Calculate the average e.m.f. induced in the coil as it turns from the position where its plane is perpendicular to the field to the position where its plane is parallel to the field. Explain, using Faraday's law, why the e.m.f. is zero in the first position and greatest in the second.
[6 marks]
(b)
The peak e.m.f. generated is 18.9 V. Calculate the r.m.s. current in the resistor and the mean power dissipated in it. Explain why the mean power is half of the peak power. State the effect on the frequency and on the peak e.m.f. of doubling the rotation rate.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).